Vacuum-type electric circuit interrupter with arc-voltage limiting means



March 5, 1968 J. w. PORTER 3,372,259

VACUUM-TYPE ELECTRIC CIRCUIT INTERRUPTER WITH ARC-VOLTAGE LIMITING MEANS Filed May 28, 1965 2 Sheets-Sheet 1 uvvnvron: JOSEPH W PORTf/i',

ATTORNEY March 5, 1968 J. w. PORTER 3,372,259 VACUUM-TYPE ELECTRIC CIRCUIT INTERRUPTER WITH Filed May 28 1965 ARC-VOLTAGE LIMITING MEANS 2 Sheets-Sheet 2 F/Go.

JOSEPH W. PoR TER,

United States Patent VACUUM-TYPE ELECTRIC CIRCUIT INTER- RUPTER WITH ARC-VOLTAGE LIMITING MEANS Joseph W. Porter, Media, Pa., assignor to General Electric Company, a corporation of New York Filed May 28, 1965, Ser. No. 459,657 9 Claims. (Cl. 200-144) ABSTRACT OF THE DISCLOSURE A high current, A-C circuit interrupter of the vacuum type, comprises a first electrode and a second electrode of gene-rally annular form surounding the first electrode in radially-spaced relationship to define an annular vacuum gap therebetween. During interruption, an are extending radially of the annular gap is developed and driven circumferentially of the gap. The are voltage developed by the circumferentially-moving arc is limited by a magnetic field that has its lines of force extending across the annular gap about its entire circumference in a radial direction.

This invention relates to an alternating current electric circuit interrupter of the vacuum type and, more particularly, to a vacuum-type circuit interrupter in which the arc voltage developed by high current arcs is held to a relatively low value.

In application S.N. 328,656, Lee, filed Dec. 6, 1963, and assigned to the assignee of the present invention, it is pointed out that the arc voltage developed by an arc during high instantaneous. currents can be appreciably reduced by applying to the are an intense magnetic field that has its lines of force extending axially of the are. The aforesaid Lee application is now abandoned but was replaced by a continuation-in-part application that issued as Patent 3,321,599. The vacuum interrupter illustrated in the Lee application employs for this purpose a magnetic field that extends axially of its contacts or electrodes.

An object of the present invention is to provide a new and improved contact or electrode arrangement in which a radial magnetic field can be used for reducing the arc voltage developed during high instantaneous currents.

Another object is to provide an electrode arrangement in which the arc is free to move circumferentially about the periphery of one of the electrodes while its arc voltage is being limited by a magnetic field applied generally parallel to the are.

In carrying out the invention in one form, I provide an alternating current circuit interrupter of the vacuum type that is adapted to interrupt currents having a maximum instantaneous value greater than 20,000 amperes. This interrupter comprises a first electrode, a second electrode of generally annular form surrounding the first electrode, and an evacuated envelope surrounding the electrodes. Means is provided for locating the electrodes in radially spaced-apart relationship to each other during a circuit interrupting operation to define a generally annular vacuum gap therebetween across which an are extending generally radially of said annular gap is established. Means is further provided for developing a magnetic field that has its lines of force extending across the annular gap about its entire circumference in a generally radial direction. This magnetic field is controlled in such a manner that its flux density in the region of the arc during instantaneous arcing currents greater than 20,000 amperes will be high enough to substantially reduce the arc voltage as compared to the arc voltage normally developed without said magnetic field extending radially of 3,372,259 Patented Mar. 5, 1968 the gap. Additional means is provided for substantially eliminating the magnetic field during the period just prior to current zero following an instantaneous arcing current greater than 20,000 amperes.

For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a sectional view of a vacuum type circuit interrupter embodying one form of the invention.

FIG. 1a is a side elevational view of a portion of the interrupter shown in FIG. 1.

FIG. 2 is a sectional view along the line 2-2 of FIG. 1.

FIG. 3 is a side elevational view partially in section illustrating the magnetic field developed by current flowing through the depicted structure.

FIG. 4 illustrates a modified form of the invention.

FIG. 5 is a sectional view along the line 5-5 of FIG. 4.

Referring now to the interrupter of FIG. 1, there is shown a highly evacuated envelope 10 comprising a tubular casing 11 of suitable insulating material and a pair of end caps 12 and 13 closing off the ends .of the casing. Suitable seals 14 are provided between the end caps and the casing to render the envelope vacuum tight. The normal pressure within the envelope 10 is lower than 10 mm. of mercury, so that a reasonable assurance is bad that the mean free path for electrons will be longer than the potential breakdown paths in the envelope.

Located within the envelope 10 is a pair of relatively movable contacts, or electrodes, 17 and 18 shown in FIG. 1 in their separated or opened-circuit position. One of the contacts 17 is a stationary contact of a generally annular form, and the other contact 18 is a movable cpntact in the shape of a round disk. The movable disk-shaped contact 18 is surrounded by the annular stationary contact 17. When the circuit interrupter is in its closed position, the movable contact 18 occupies the dotted line position 20 of FIG. 1. In this position, the outer periphery of contact 18 bears against the inner periphery of annular contact 17, and the region of engagement forms a contact point through which current can flow between the contacts 17 and 18.

When the circuit interrupter is to be opened, the inner contact 17 is moved generally radially from its dotted line position 20 to the solid line position shown in FIG. 1. This radial contact movement establishes an annular gap 22 between the contacts 17 and 18, and across this gap 22 a radially-extending are 24 is developed. This are 24 is subsequently extinguished, thereby interrupting the circuit, in a manner that will soon be described.

The movable contact 18 is suitably joined to the upper end of a conductive operating rod 30. This operating rod 30 is pivotally mounted on a stationary pivot 31 located externally of the envelope. When the circuit interrupter is to be opened, the rod 30 is pivoted in a clockwise direction from its dotted line position of FIG. 1 into its solid line position, thereby moving the contact 18 to its solid line position. Closing is effected by returning the rod 30 and contact 18 to their dotted line positions. This pivotal operating motion of the rod 30 is produced by a suitable mechanism (not shown) coupled to the lower end of the operating rod.

The operating rod 30 projects through an opening in the lower end cap 13, and a flexible metallic bellows 34 provides a seal about the rod 30 to allow for the abovedescribed pivotal operating movement of the rod without impairing the vacuum inside the envelope 10. As shown in FIG. 1, the bellows 34 is secured in sealed relationship at its respective opposite ends to the operating rod 30 and the end cap 13.

The stationary annular contact 17 is mounted on a conductor 40 of high conductivity material, such as copper,

that is spirally wound into a coil of generally cylindrical form. This conductor 40 has an extension 40a at its upper end that extends through the end cap 12 and serves as one terminal of the interrupter. A suitable brazed joint 42 is provided about the extension 40a to maintain the envelope vacuum-tight and to provide a mechanically strong connection between the end cap 12 and the extension 40a.

For reasons which will soon be pointed out, the end caps 12 and 13 are made of a high resistivity, non-magnetic material, such as stainless steel. A suitable brazed joint is provided along the upper end surface of the coil 40 and the stainless steel plate 12 to provide a mechanically strong joint between these parts. Because the end cap 12 is of a material having a very high resistivity compared to that of the copper, practically all of the current entering and leaving the coil 40 at its upper end does so through the extension 40a.

For structurally reinforcing the coil 40 to increase its resistance to bending and other types of deformation, a plurality of stainless steel spacers 44 are provided between the adjacent turns of the coil. These stainless steel spacers 44 are preferably held in position between the turns by suitable brazed joints provided along the contiguous surfaces of the spacers and the turns. Since stainless steel has a very high resistivity in comparison to that of the copper used for conductor 40, very little of the current fiows through the spacers. Nearly all the current is forced to follow this spiral path followed by the conductor 40.

Current following the spiral path through the conductor 40 produces a magnetic field of the general configuration shown at 50 in FIG. 3. This field 50 has its lines of force 51 extending axially of the coil 40 along the length of the coil and radially of the coil at its longitudinal ends. In extending radially of the coil 40 at its lower end, the lines of force 51 extend in a radial direction across the annular gap 22, as shown most clearly in FIG. 2. Since the arc 24 also extends generally radially of the gap 22, it will be apparent that the lines of force 51 of the magnetic field that are immediately adjacent the arc extend generally parallel to the arc.

As pointed out in the aforementioned Lee application, the arc voltage developed by a vacuum arc at high instantaneous currents can be effectively limited by locating the arc in a strong magnetic field that extends axially of the arc. For instantaneous currents in excess of about 30,000 to 40,000 amperes, it appears that the field strength required for a given reduction in arc voltage increases as the peak current increases. It also appears that for a given current there is a field strength above which increased field strength has little effect in further reducing arc voltage.

In a preferred form of the invention, the field strength of a magnetic field is made high enough to reduce the arc voltage developed during peak currents above 40,000 amperes to less than one-half the arc voltage that would be developed for corresponding peak currents without the magnetic field. But if higher are voltages can be tolerated, a reduced field strength can be employed. In any case, however, I use a field strength greater enough to produce a substantial reduction in arc voltage for instantaneous currents above 20,000 amperes. By way of example, in one embodiment of the invention, I provide a field producing coil 40 that can develop in the arcing gap 800 gausses at 20,000 amperes, 1,600 gausses at 40,000 amperes, and 2,400 gausses at 60,000 amperes.

By reducing the arc voltage developed under high current conditions, it is possible to improve the interrupters ability to condense the arcing products, thereby improving its ability to Withstand the usual recovery voltage developed immediately following current zero. For condensing the arcing products, a tubular metallic shield 60 is relied upon. This shield surrounds the arcing gap 22 and is preferably electrically isolated from both contacts 17 and 18. The ability of shield 60 to condense the arcing products depends to an important extent upon its temperature, and generally speaking, improves with reduced temperatures. By reducing the arc voltage developed during high currents, I reduce the energy input into the shield 60 during this interval, thus reducing the shield temperature and improving its vapor-condensing abilities.

But to increase the circuit interrupting capacity of a vacuum interrupter, it is not enough merely to maintain across the gap a strong axial magnetic field that reduces the peak arc voltages. This is the case because the presence of a strong magnetic field extending parallel to the arc during the period when the arcing current is approach ing zero can seriously impair the current interrupting ability of the vacuum interrupting even though the arc voltage during high values of instantaneous current had been reduced. Thus, I control the magnetic field extending parallel to the arc in such a manner that it is substantially eliminated during current zero and the period immediately preceding it. It is not necessary to completely eliminate the axial magnetic field during this crucial period, but its field strength should be reduced to a sufficiently low value that there is no substantial impairment of the recovery voltage withstand ability of the arcing gap as compared to that of the gap without an axial magnetic field during this interval around current zero.

Since the coil 40 of FIG. 1 is in series with the contacts 17, 18 of the interrupter, it will be apparent that current through the coil and the arcing current are in phase. This, however, does not automatically assure that the magnetic field or flux produced by the coil 40 in the arcing gap will be in phase with the arcing current. Unless the eddy currents induced by the magnetic current are held to a low value, they will cause an appreciable lag in the flux behind the current, and this will result in a relatively high magnetic field remaining across the gap when the current zero point is reached. To reduce these eddy currents to such a level that the fiux and the arcing current are approximately in phase, I form the end caps 12 and 13 of a high resistivity, low permeability material, such as stainless steel, and I utilize slots 62 and 64 in the contacts 17 and 18 to break up the eddy current paths through the contacts. With regard to this latter feature, I extend the slots 64 in contact 18 radially inward as far as possible so as to improve their effectiveness in breaking up the eddy current paths. In addition, the contact 18 is perforated in its central region, as shown at 65 in FIG. 2, to further reduce the eddy currents. Still further, I form the shield 60 of high resistivity, low permeability material such as stainless steel. If a low resistivity metal is used for the shield 60, the shield 60 should be provided with suitable eddy current suppressing means, such as shown for example in my joint application with G. Polinko, S.N. 454,282, now Patent No. 3,345,484 filed may 10, 1965, and assigned to the assignee of the present invention.

With the eddy currents so reduced, the flux is maintained sufliciently in phase with the arcing current to provide a low enough field strength at and just before current zero to prevent any substantial impairment of the gaps recovery voltage withstand ability at current zero.

Suitable end shields 60a and 60b of tubular form are provided at opposite ends of the main shield 60 to intercept any arc-generated vapors that might enter these regions.

An advantage of the concentric contact arrangement of my interrupter is that the arc is not confined to any fixed position on the contact. An arc that is disposed in a strong magnetic field extending axially thereof appears to have a tendency to move into a position where the axial field is weakest. But in the disclosed interrupter the magnetic field extending across the inter-contact gap 22 axially of the arc has substantially the same strength about the entire periphery of the disk-shaped contact 18. Thus, the arc is not confined by the magnetic field 50 to any fixed location on the periphery of the contact 18. It can move in a circumferential direction about the periphery of the contact 18.

To encourage arc movement about the periphery of contact 18, I form the slots 64 of the configuration best shown in FIG. 2. These slots force current flowing through the contact 18 to or from an arc terminal on the contact periphery to follow a path that extends generally tangentially of the arc in the immediate vicinity of the arc. The magnetic efiect of current following such a tangentially extending path is to urge the arc in a circumferential direction about the contact periphery.

The single slot 62 in the outer contact 17 also forces the current path through this contact to have a tangentially-extending component in the region of the arc. The electrical connection between the conductor 40 and the contact 17 is located immediately adjacent the slot 62 and thus current through the contact 17 to an arc terminal follows a path that always extends in the same circumferential direction regardless of the angular position of the arc on the contact 17. Stainless steel spacers 44 of appropriate size are brazed between the lower end of the coil and the split annular contact 17 to provide a mechanically strong connection between these parts without introducing a low resistance path bridging slot 62.

In order to provide for increased field strength in the radial magnetic field extending across gap 22, I can use a plurality of coils instead of the single coil 40 shown in FIG. 1. FIG. 4, for example, shows an arrangement using two coils 40 and 40b disposed in colinear relationship when the interrupter is open. The coil 40 is identical to the coil 40 of FIG. 1, but the coil 40b is wound in an opposite direction to the coil 40. In other respects, coil 40b is constructed similarly to coil 40. The two electrodes 17 and 18b of FIG. 4 are annular electrodes disposed in generally concentric relationship to each other when the interrupter is open. Annular electrode 17 is electrically connected to coil 40 and is rigidly supported thereon in the same manner as in FIGS. 1-3. Annular electrode 18b is electrically. connected to coil 40b and is rigidly supported thereon in the same manner as the other electrode is supported on its coil. Each electrode is disposed in colinear relationship to its coil and is provided with a slot 62, as shown in FIG. 5, rendering it circumferentially discontinuous. Each of these slots '62 corresponds to the slot 62 of FIG. 1a and serves the same basic purpose, i.e., to prevent eddy currents from. finding a path extending circumferentially of the electrode.

When the circuit interrupter of FIG. 4 is closed, the electrodes engage each other in the same manner as the electrodes of FIG. 1. Opening is elTected by moving the inner electrode 18b laterally inward into its depicted position of FIG. 4. This establishes between the two electrodes an are 24 that extends radially across the annular gap 22 that is developed between the two electrodes.

Current flowing through the arc 24 also flows through the two coils 40 and 40b which are in series therewith. Since the coils are oppositely wound, as abovedescribed, they develop magnetic fields 50 and 50b of the approximate configuration illustrated in FIG. 4. Along the central axis of the coils 40 and 40b, the magnetic fields 50 and 50b of the two coils extend axially of the coils in opposite directions at any given instant. But in the region between the two coils, the two fields 50 and 50b extend in the same radial direction. Thus, in the region between the'two coils, the fields are additive, and an especially high strength field is developed in this region. The annular gap 22 is so located that the two fields extend radially thereacross in this high field strength region between the coils Where the fields are additive. This composite field 50, 50]; extends radially of the annular gap 22 about the entire periphery of electrode 18b and has substantially the same strength about this entire periphery. The are 24 extends parallel to the portion of this field immediately thereadjacent in the same manner as illustrated in FIG. 2. Thus, the magnetic field limits the are voltage during high instantaneous currents, as described hereinabove. Since the field has substantially the same strength about the entire periphery of the electrode 18b, the arc is not confined by the magnetic field to any circumferentially fixed location on the electrode peripheries.

The slots 62 in the electrodes 17 and 18b of FIG. 5 force the current flowing through each electrode to or from an arc thereon to follow a tangentially extending p'ath in the imediate region of the arc, and this promotes arc motion over a circular path along the electrodes, as pointed out hereinabove.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects; and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An alternating current circuit interrupter of the vacuum type that is adapted to interrupt currents having maximum instantaneous values greater than 20,000 amperes comprising:

(a) a first electrode,

(b) a second electrode of generally annular form surrounding said first electrode,

(c) an evacuated envelope surrounding said electrodes,

(d) means for locating said electrodes in radially spaced-apart relationship to each other during a circuit interrupting operation to define a generally annular vacuum gap therebetween across which an arc extending generally radially of said annular gap is established,

(d) arc-motivating means for driving the arc circumferentially of said gap,

(e) means for developing a magnetic field that has its lines of force extending across said annular gap about its entire circumference in a generally radial direction,

(f) means for controlling said magnetic field in such a manner that its flux density in the region of the arc during instantaneous arcing currents greater than 20,000 amperes will be high enough to substantially reduce the arc voltage as compared to the arc voltage normally developed without said magnetic field extending radially of the gap,

(g) and means for substantially eliminating said magnetic field during the period just prior to current Zero following an instantaneous arcing current greater than 20,000 amperes.

2. The circuit interrupter of claim 1 in which the means for substantially eliminating said magnetic field just prior to current zero comprises eddy current suppressing means for suppressing eddy currents induced in said electrodes by said magnetic field, said eddy current suppressing means comprising discontinuities in said electrodes which interrupt conductive paths extending circumferentially of said electrodes.

3. The circuit interrupter of claim 1 in which said magnetic field has a high enough density for instantaneous currents above 40,000 amperes to reduce the instantaneous arc voltage for such currents to less than half the arc voltage developed when no magnetic field extending radially of said gap is present.

4. The circuit interrupter of claim 1 in combination with means for establishing a solid conductive path between said electrodes when said circuit interrupter is in a closed condition.

5. The circuit interrupter of claim 1 in which said electrodes are relatively movable from a position of engagement to a position of disengagement, and in which means is provided for moving one of said electrodes laterally with respect to the other to establish said generally annular arcing gap.

6. The circuit interrupter of claim 1 in which said means for developing said magnetic field comprises a coil connected in series with said electrodes so that the arcing current flows through said coil.

7. A vacuum type circuit interrupter comprising:

(a) a first electrode,

(b) a second electrode of generally annular form surrounding said first electrode,

(c) an evacuated envelope surrounding said electrodes,

(d) means for locating said electrodes in radially spaced-apart relationship to each other during a circuit interrupting operation to define a generally annular vacuum gap therebetween across which an are extending generally radially of said annular gap is established,

(d) arc-motivating means for driving the arc circumferentially of said annular gap,

(e) and means for substantially reducing the arc voltage developed by an arc during high current interruptions comprising means for developing an intense magnetic field that extends across said annular gap about its entire circumference in a generally radial direction.

8. The interrupter of claim 7 in combination with means for substantially eliminating said magnetic field during the period just prior to current zero following an instantaneous arcing current greater than 20,000 amperes.

9. An alternating current circuit interrupter of the vacuum type that is adapted to interrupt currents having maximum instantaneous values greater than 20,000 amperes comprising:

(a) a first electrode,

(b) a second electrode of generally annular form surrounding said first electrode,

(c) an evacuated envelope surrounding said electrodes, 35

(d) means for locating said electrodes in radially spaced-apart relationship to each other during a circuit interrupting operation to define a generally annular vacuum gap therebetween across which an are extending generally radially of said annular gap is established,

(e) means for developing a magnetic field that has its lines of force extending across said annular gap about its entire circumference in a generally radial direction,

(f) means for controlling said magnetic field in such a manner that its flux density in the region of the arc during instantaneousarcing currents greater than 20,000 amperes will be high enough to substantially reduce the arc voltage as compared to the arc voltage normally developed without said magnetic field extending radially of the gap,

(g) means for substantially eliminating said magnetic field during the period just prior to current zero following an instantaneous arcing current greater than 20,000 amperes, and

(h) said means for developing said magnetic field comprising a pair of coils connected in series with said electrodes, said coils being arranged to develop individual magnetic fields that, at a given instant, extend axially of said electrodes in generally opposite directions but radially of said electrodes in the same directions; said annular gap being so located that both of said individual fields extend radially thereof in the same general direction at a given instant.

References Cited UNITED STATES PATENTS Re. 21,087 5/1939 Rankin 200-144 2,027,833 1/1936 Rankin 200 -144 3,014,109 12/1961 Burger 200-144 3,082,307 3/1963 Greenwood 200-144 3,283,103 11/1966 Greenwood 200-144 ROBERT S. MACON, Primary Examiner. 

